I've always been a little surprised they barely use the Leader as a major threat in the comics considering he's basically as smart as the Hulk is strong, therefore I'd assume he's smarter than both Reed & Doom making him very dangerous indeed.

People often make that claim, but the Leader has never done *anything* to back it up. He may well be smarter than the likes of Stark and Pym, but the absolute best feats of his entire career barely compare with typical ones from the Reed/Doom pair.

Or, there is a guy smart enough to literally bust into the Gates of Heaven to bring back the dead. His name is not 'Leader'.